/Engine/Source/Runtime/CoreUObject/Public/Serialization/FindObjectReferencers.h
Each key corresponds to an element of the input TargetObjects array which was referenced by some other object. The values for these keys are the objects which are referencing them.
template<class T> class TFindObjectReferencers : public [TMultiMap< T *, UObject * >](API\Runtime\Core\Containers\TMultiMap)